Field of the Invention
The invention relates to a communication system and a routing method thereof, in particular, to a vehicular communication system and a routing method thereof.
Description of Related Art
Traditional routing protocols in vehicular ad hoc networks (VANETs) are node-based, while to adapt to urban VANETs, most of recent routing protocols are road-based. In node-based routing protocols, a path is composed of nodes, and packets are relayed along the determined sequence of nodes. However, due to high mobility in VANETs, nodes move apart from each other rapidly. The physical link of consecutive relay nodes easily gets broken so that route failures occur frequently in node-based routing protocols. Frequent rout failures result in packet loss and increase control overhead of route recovery. As a result, road-based routing protocols were proposed to improve route stability. That is, a path consists of a succession of road sections from source to destination, and data packets are transferred along the road sections. With each road sections, geographical forwarding is used. As long as nodes are dense enough in each road section of a path, the whole path is connected. In urban VANETs, node density in a road section does not vary too much, in a short period. Therefore, road-based routing is steadier than node-based routing. To further enhance route stability, multipath routing provides alternative routes immediately once the current route fails, or provides concurrent transmission with multiple paths. However, existing multipath routing approaches are node-based routing protocols. So they still inherit the drawback of node-based routing protocols that nodes move apart from each other rapidly.